Phytoplankton community diversity along a river-estuary continuum

Abstract

In this paper we examine the aspects of phytoplankton communities along a riverine-estuarine continuum in the Kowie system, Eastern Cape (South Africa). This study aims to relate the phytoplankton population community structure to physicochemical parameters and estimate the different chlorophyll-a concentrations for the Kowie system. Eight sampling sites along a 70 km reach of the Kowie system were sampled over a one-year period. One hundred and seventy-eight species belonging to 78 genera were recorded within the riverine-estuarine continuum. Diatoms were predominant, accounting for 81.9% of the total abundance. The estuary had 98 species (55 genera) recorded whereas the river had 141 species (67 genera). Using a two-way analysis of variance (ANOVA), species richness was found to differ significantly amongst seasons. The chl-a concentration along the estuarine-riverine continuum increased from spring to a high in summer (river mean = 7.9 mg m⁻³ and estuary mean = 3.3 mg m⁻³) before decreasing to a low in winter. Kruskal–Wallis ANOVA showed significant differences among chl-a concentration with seasons and sites. Redundancy analysis identified five factors – salinity, water depth, aerial cover, nitrates and ammonia – that were significant (p < 0.05) in affecting phytoplankton variation. The relatively small study indicates the need for further monitoring to gain a better understanding of Kowie system phytoplankton.

Keywords:

• ANOVA
• diatoms
• chlorophyll-a
• Kowie system
• river continuum concept
• salinity

ACKNOWLEDGEMENTS

This work was supported by the Water Research Commission of South Africa (WRC), National Research Foundation of South Africa (NRF) and Rhodes University. The Eastern Cape Department of Economic Development, Environmental Affairs and Tourism (permit no. CRO 116/12CR) provided collection permits. We are grateful to Jonathan C. Taylor, North-West University for helping with the diatom identification manuals and methods, Jeff Hean, Katherine Schoo, Matthew Parkinson, Lenin D Chari, Leandro Bergamino, Simphiwe Gininda, Likho Sikutshwa, Sydney Moyo and Jakob Katzenberg for assistance during field work.